puyopuyotetr.is/app/javascript/mastodon/features/compose/containers/upload_button_container.js

import { connect } from 'react-redux';

import { uploadCompose } from '../../../actions/compose';
import UploadButton from '../components/upload_button';

const mapStateToProps = state => {
  const isPoll = state.getIn(['compose', 'poll']) !== null;
  const isUploading = state.getIn(['compose', 'is_uploading']);
  const readyAttachmentsSize = state.getIn(['compose', 'media_attachments']).size ?? 0;
  const pendingAttachmentsSize = state.getIn(['compose', 'pending_media_attachments']).size ?? 0;
  const attachmentsSize = readyAttachmentsSize + pendingAttachmentsSize;
  const isOverLimit = attachmentsSize > 3;
  const hasVideoOrAudio = state.getIn(['compose', 'media_attachments']).some(m => ['video', 'audio'].includes(m.get('type')));

  return {
    disabled: isPoll || isUploading || isOverLimit || hasVideoOrAudio,
    resetFileKey: state.getIn(['compose', 'resetFileKey']),
  };
};

const mapDispatchToProps = dispatch => ({

  onSelectFile(files) {
    dispatch(uploadCompose(files));
  },

});

export default connect(mapStateToProps, mapDispatchToProps)(UploadButton);